DEV: do not return no_result_help from the server (#15220)

We don't need it anymore. Actually, I removed using of it on the client side a long time ago, when I was working on improving blank page syndrome on user activity pages (see https://github.com/discourse/discourse/pull/14311).

This PR also removes some old resource strings that we don't use anymore. We have new strings for blank pages.

app/controllers/drafts_controller.rb

@@ -16,8 +16,7 @@ class DraftsController < ApplicationController
     )
 
     render json: {
-      drafts: stream ? serialize_data(stream, DraftSerializer) : [],
-      no_results_help: I18n.t("user_activity.no_drafts.self")
+      drafts: stream ? serialize_data(stream, DraftSerializer) : []
     }
   end
 

app/controllers/user_actions_controller.rb

@@ -25,20 +25,7 @@ class UserActionsController < ApplicationController
     }
 
     stream = UserAction.stream(opts).to_a
-    if stream.empty? && (help_key = params['no_results_help_key'])
-      if user.id == guardian.user.try(:id)
-        help_key += ".self"
-      else
-        help_key += ".others"
-      end
-      render json: {
-        user_action: [],
-        no_results_help: I18n.t(help_key)
-      }
-    else
-      render_serialized(stream, UserActionSerializer, root: 'user_actions')
-    end
-
+    render_serialized(stream, UserActionSerializer, root: 'user_actions')
   end
 
   def show

app/controllers/users_controller.rb

@@ -1621,10 +1621,7 @@ class UsersController < ApplicationController
 
         if bookmark_list.bookmarks.empty?
           render json: {
-            bookmarks: [],
-            no_results_help: I18n.t(
-              params[:q].present? ? "user_activity.no_bookmarks.search" : "user_activity.no_bookmarks.self"
-            )
+            bookmarks: []
           }
         else
           page = params[:page].to_i + 1